The proposed research is designed to obtain information about social network factors which influences initiation, maintenance and discontinuation of IV drug user (IVDU) needle sharing behavior (NSB) and AIDS prevention behavior (APB). The hypothesis under consideration are that NSB is positively and (APB) negatively associated with membership in needle sharing networks characterized by norms approving needle sharing and disapproving APB. Further that more cohesive networks will demonstrate greater conformity to NSB and APB norms. This hypothesis will be tested by systematic interviews with all members of 156 randomly selected needle sharing networks. The casual association of needle sharing network norms on APB will be tested through a random assignment preventive trial using as subjects needle sharing networks assigned to an intervention procedure aimed at modifying network APB norms compared to an analogous individually oriented intervention. Geographic clustering of networks with norms for or against APB will be examined in relation to clustering of HIV-1 infection in Baltimore to determine their association. The geographic distribution of structural and functional characteristics of needle sharing networks will also be examined as a potential explanatory variable for geographic variation in needle sharing behavior and HIV rates.